For the distortion measurements, I placed the microphone 1 foot from the center of the respective driver.

At 20 Hz and 90 dB output, THD+N was 8%.

At 50 Hz, distortion plummeted to less than 0.5%.

At 1 kHz, distortion was 0.2%, and this was coming from a 15" driver rather than the usual 5.25" midrange driver found in most speakers. Not bad at all !

Measured from the tweeter, a 9 kHz signal at 90 dB produced less than 0.5% distortion. Excellent performance!

The room frequency response, measured at a distance of 3 meters, is shown below. The peaks and dips are due to the room, so if we take an average, it appears to be reasonably flat down to about 70 Hz, when it declines. There is a small amount of boost between 700 Hz and 1 kHz, which would make the midrange a bit forward. Like just about every full-range speaker, the Athenaeum would benefit from a dedicated subwoofer to take care of the lowest octave.

The Athenaeum is a very easy speaker to drive, not only because of its sensitivity, but because it has a nominal impedance of about 10 ohms. However, because these are ultra-high-end speakers - at 60 Large for the pair - I suggest that you upgrade your $799 receiver that you got from Amazon, and go with a pure Class A triode preamp and power amplifier (or integrated), somewhere in the neighborhood of about 30 watts per channel or so.